It is frustratingly hard work to buy plus size clothes that are decent quality and interesting. I agree with @MuddlerInLaw on Marina Rinaldi - I tend to buy in sales as it can be £££ but the cutting is great and there are some interesting clothes (also some not so interesting stuff - so definitely sift.)
I find M&S autograph good for more classic pieces in good quality fabrics - silk and cotton shorts, wool etc. I have an excellent pair of straight leg, slightly mannish, selvedge jeans that were reasonable and I love. But I don’t like the fit in more tailored jackets etc — they feel like scaled up small garments, rather than pieces cut for bigger bodies.
Also sometimes surprisingly good for quality fabrics is H&M plus - I had a couple of great shirts from there this summer that fit well, have drape, and make a good solid nod to current trends.
I often find Anna Scholz a bit frilly for my taste, but I have an excellent pair of wide leg trousers from her I’ve worn a lot, and I’ve just ordered a midi-dress in the sale that looks promising.
Mango is good for tailoring and more interesting pieces - I bought a brilliant summer co-ord that I have really loved. Quality is a bit variable. V well cut T-shirts, interestingly.
tbh I am uninspired by lots of what’s on offer right now. I’m hoping there is some interesting new stuff coming - or if not, this might be a season for rediscovering stuff I already have and making it work hard with new accessories. Good shoes, hair and jewellery can make fairly basic outfits look more relevant. (Well I hope they can!)
I have been enjoying wearing a new (to me) silhouette this summer of high-waist, wide-leg trousers with a boxy cropped-ish top. Not so crop there’s any danger of skin, but deffo well above hip height. The top should be woven rather than knit - and I find more flattering than (eg) a tucked cami or similar.
Happy shopping - and definitely come back to tell us where you’ve found good stuff!